PICTURE -- Big vs. small impact wrench

http://yabe.algebra.com/~ichudov/misc/ebay/Ingersoll-Rand-Impact-Wrench/divx.video.avi
I suspect that it would have been easier to control with a well
torqued in the socket. There would have been less spinning up.
Not going to bother visiting the web site. Video is a pain to
view on this system -- especially with my preferred browser.
Enjoy,
DoN.

As an aside, has anyone seen the Milwaukee .mwv file of the sports car
racing, and pulling in for a pit stop? The mechanic takes off the wheel,
and when he goes to retorque the wheel, the whole car flips over and slams
on its roof. Very nicely done, and very realistic. I have it in my files,
but don't know how to post it. It used to be a URL.
Steve

A few weeks back at Lime Rock, I was surprised to see far, far more
18V impact drivers in the pits and garages than air versions.
I remember seeing DeWalt, Milwaukee, and Makita, with about 75%
DeWalt.
There were a mixture of teams, ranging from Joe Gibbs, Roush, and
various factory (Subaru, Acura, VW, BMW, MINI, etc...) road racing
teams, to privateers with open trailers. The use of cordless drivers
was pretty universal.
---------------------------------------------
** http://www.bburke.com/woodworking.html **
---------------------------------------------

I gotta disagree with you. Law of conservation of angular momentum -
if you're tranferring that much net torque to the target, that torque
has to pretty soon make it up to the wrench and whatever's supporting
the wrench. The rotational inertia of the wrench and plumbing will
take up some small initial amount of impact, and for some trivial uses
(lugnuts) this may be the only important torqueing it does. Not true
for a 2.5" on an oilfield!
Tim.

wrote:
I gotta disagree with you. Law of conservation of angular momentum -
if you're tranferring that much net torque to the target, that torque
has to pretty soon make it up to the wrench and whatever's supporting
the wrench. The rotational inertia of the wrench and plumbing will
take up some small initial amount of impact, and for some trivial uses
(lugnuts) this may be the only important torqueing it does. Not true
for a 2.5" on an oilfield!
Tim.
I cannot state which law comes in to play but can tell you from experience
that I have never experienced a measurable amount of feed back difference
using a 1/2" impact to remove automotive lug nuts to a 1" impact removing 2"
nuts.

An impact wrench uses the motor to spin up a big chunk of metal that
functions as a hammer. The hammer is then allowed to strike an anvil
to which the socket is attached, conveying torque to the fastener.
It's the same idea as wanging on a slugging wrench
(http://www.drillspot.com/products/67597/Proto_USN340_Slugging_Wrench
for example) with a hammer only the tool does it all for you. If it's
a big heavy hammer then the tool is going to convey some torque back
to the operator as the hammer spins up, but since the tool can take
its time about spinning up the hammer it it conveys much less force to
the operator than the tool applies to the fastener.

The principal of the impact action is the same regardless of the size.
I don't remember my mechanics very well, but I do recall that the
mathematics of "impulse" is different from simple statics. Many shots
from a BB gun can move a floating aircraft carrier but the shooter
never feels more than a minor recoil VERY many times. The energy
delivered is large but in tiny, rapid increments.

wrote:
The principal of the impact action is the same regardless of the size.
Precicely, but again that assumes tha tthe impact is operating properly.
I don't remember my mechanics very well, but I do recall that the
mathematics of "impulse" is different from simple statics. Many shots
from a BB gun can move a floating aircraft carrier but the shooter
never feels more than a minor recoil VERY many times. The energy
delivered is large but in tiny, rapid increments.
That breaks it down pretty well.

wrote in message
I gotta disagree with you. Law of conservation of angular momentum -
if you're tranferring that much net torque to the target, that torque
has to pretty soon make it up to the wrench and whatever's supporting
the wrench. The rotational inertia of the wrench and plumbing will
take up some small initial amount of impact, and for some trivial uses
(lugnuts) this may be the only important torqueing it does. Not true
for a 2.5" on an oilfield!
Tim.
wrong application - the energy transfer is to accelerate a rotary hammer
that then smacks against an anvil delivering an impluse - when the hammer
hits the anvil, neither is connected in any significant way to the handle -
so you have to hold the torque of accelerating the hammer, not the impact
torque (beause the acceleation is caused by the air motor, and the reaction
torque of the air motor is against the body of the tool)

I've never looked at the design but it's got to be a bit more complex than
that.
The rotary hammer can't just be accelerated in a single direction. It's
got to be accelerated in both directions. So after it "hits" the anvil,
it's got to be brought back for the next strike. This requires that the
hammer transfer torque in both directions. As a result, the net torque
sent to the operator can in theory be zero. To make that actually work,
the wrench would need have at least two moving parts - like two hammers
which were taking turns making the strikes and using the momentum of each
other to move - with a net transfer of zero torque to the operator. I
don't know if real torque wrenches work that way, but you would think those
really large ones would almost have to work that way - or else just require
they have long handles with two operators to absorb the torque.
I think my logic on this is correct - but maybe I'm just crazy....

Yeah, I was just going to look to see if wikipedia had an article on them.
Very interesting, thanks.
That last design they describe with the "rocking hammer" I couldn't really
understand from the description they gave but it sounded a bit like what I
was thinking including the idea of using two hammers.
On the standard design however, it's clear that the torque to spin up the
hammer is constantly being transfered to the operator and the reason it
doesn't produce as much torque as delivered to the nut is simply because
the energy is stored up over a longer period of time as it spins up the
hammer and then delivered in a very short period of time to the nut at a
much higher torque. As was already said, it's just like using a hammer
where the impact of the hammer creates a much greater force than the
operator had to apply to the hammer.
Didn't NASA have to design powered wrenches that would work in space
without causing the astronaut to spin in cycles?

I recall that they had come up with some designs, but it looks like
what happens in the real world is that the astronaut secures himself
somehow. The Hubble Space Telescope has special mounting points for
the foot-braces that are used during servicing.

Log in

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.